The present invention relates to an advanced process for refining (the term "purification" is used sometimes as a synonym for "refining" hereinafter) quartz powder. More specifically, the present invention relates to a process for continuously refining quartz powder to provide a high purity starting material suitable for use in the fabrication of silica glass vessels and jigs that are essential in the semiconductor industry, and which is also suitable for silica fillers to be added into plastic packages.
Quartz powder, and particularly the powder of naturally occurring quartz, has been utilized heretofore as a starting material of quartz glass materials for fabricating silica glass vessels or jigs, as well as of silica fillers to be added into plastic packages such as ICs and LSIS. However, it has been found that those quartz powders contain various types of impurities, and that the impurities unfavorably influence the semiconductor products. Attempts have been made to purify the quartz powder accordingly. For instance, the specification of U.S. Pat. No. 4,956,059 discloses a process which comprises bringing the starting quartz powder into contact with a chlorine-containing gas atmosphere in a temperature range of from 700.degree. to 1,300.degree. C. in a reaction tube while applying voltage thereto. JP-A-48-69794 (the term "JP- A-" as referred herein signifies "an unexamined published Japanese patent application") discloses refining a powder of rock crystal by bringing it into contact with chlorine or a gas containing chlorine at a temperature in a range of from 700.degree. to 1,300.degree. C.
The purification process as disclosed in the aforementioned U.S. Pat. 4,956,059 is certainly a method for refining naturally occurring quartz to a high level of purity. However, the whole process is costly not only because it comprises steps of batch processes, but also because voltage is applied to the reaction tube. Concerning the purification process disclosed in JP-A-48-69794, it was found impossible to sufficiently purify a powder of a naturally occurring quartz. More specifically, alkali metal elements, alkaline earth metal elements, transition metal elements, radioactive elements, etc., that are inherent in the naturally occurring quartz were not sufficiently excluded therefrom. In particular, alkaline each metal elements and transition metal elements were found to remain in quartz after the purification according to this process. Accordingly, it was not possible to achieve a high purity quartz required in the present day semiconductor industry.